If it's night time, stay on the surface, or better, decks awash. Slow to half ahead when you get within 1000 meters of the DDs. You can pass undetected within 500 m of them.

In the day time, go to peri depth at 5,500 m. from the DDs. Keep peri down. When you must check your position - and theirs - slow down, raise peri just enough to break the surface... so that waves wash over the lens. Lower it as soon as you have refreshed your plot view. Go no faster than Ahead 1/3 or even Slow or All Stopped if a DD might detect you, 2,2000 m or closer. Keep your U-boat pointed at the nearest DD to reduce your SONAR profile to him; be ready to fire a torp if he's charging you. Go Flank speed and fire at 400 or 300 m. and immediately crash dive and a maximum turn of 90 degrees. As the depth charges go off, click on your depth gauge to return to peri depth. Resume approach to convoy, but keep an eye on that DD to see if he comes back. Keep your speed down, and stern or bow pointed at him if he might hear you.